Comparative studies on biological activity of certain microtubule-interacting taxanes

We have compared the nature of interaction of certain taxanes with microtubular protein, and the mechanism of action underlying cytotoxic activity. Taxanes induced tubulin assembly in vitro, but only taxanes bearing side chain were capable of inducing the formation of stable tubulin polymers. Electron microscopy detections showed that taxane-induced polymers are structurally similar to microtubules formed by paclitaxel, with differences in length. Otherwise, light microscopy views have shown that intracellular microtubule network is deeply reorganized by taxanes into short fibers, unlike paclitaxel-bundled microtubules. Taxanes inhibited the growth of various human tumor cell lines, but cell cycle analysis did not always indicate a block in the G2/M phase. These agents alter some apoptotic signal transduction pathways, probably by a mechanism distinct from microtubule interaction. Briefly, the effectiveness of taxanes is closely related to their chemical structure, and depends on their interaction with microtubular protein. By virtue of this mechanism, some of these taxanes may provide usefulness for therapeutic improvements.